TRENTON — More than 40 towns and counties today scrambled to make sure their police and firefighters can’t get bigger raises now that a law that has kept them low is about to expire, according to a state lawmaker.

On Tuesday, a state law in effect since 2011 that caps interest arbitration awards at 2 percent — compensation given out by third party arbitrators when governments and police and fire unions can’t reach a contract agreement — will sunset.

Today, according to state Assemblyman Declan O’Scanlon (R-Monmouth), dozens of local governments that had been negotiating contracts with the unions dropped the talks and filed for arbitration.

“This action was necessary as a precaution to insulate property tax payers from any impact of the arbitration award cap expiration. There is the potential that some labor unions may be tempted to file frivolous law suits in an attempt to take advantage of the interest arbitration cap expiration,” O’Scanlon said in a statement. “The action these bargaining units took today will help to make doubly sure they won’t be vulnerable to such action.”

The state Senate and Assembly on Thursday sent Gov. Chris Christie a bill that would extend the cap until the end of 2017, but would significantly loosen it. Christie conditionally vetoed it, putting it largely in line with current state law. But while the state Senate concurred with his recommendations, the Assembly left town and does not plan to return any time soon.

“It’s disgraceful that the Assembly didn’t follow suit,” said O’Scanlon (R-Monmouth), who has led the push to renew the law.

When the law expires, it’s unclear if the cap will apply to contracts that are under negotiation but have not yet gone into arbitration.

“But in this day and age, taking the precaution is the best thing to do,” O’Scanlon said.

O’Scanlon attributed his figures to the New Jersey Public Employment Relations Commission. O’Scanlon said he did not have a list of counties and municipalities that have filed, though he said Monmouth County is among them.

The commission’s chairwoman, Kelly Hatfield, said in a phone interview she was out-of-state and did not immediately have the numbers on hand.

The state League of Municipalities today wrote a letter to mayors urging them to lobby legislators to get back to Trenton and pass an extension.

“Also, if you have an unsettled Police or Fire contract we suggest you contact your labor attorney to discuss your options before the April 1 deadline,” League executive director Bill Dressel wrote.